Numerous biotechnological processes make use of genetically engineered organisms in order to produce bulk or fine chemicals, proteins or antibiotics. In many cases, increased production has been obtained by improved gene expression and by optimization of growth conditions. In most processes, the initial carbon-precursor has been and still is sugar (notably glucose, but many other mono- and polysaccharides are in use) or related organic substrates: solventogenesis (including butanol and ethanol) and organic acid production (e.g. lactic-, citric- or succinic acid) always starts from glucose, which makes it inefficient as the production process uses a high energy compound as input substrate.
Standard fermentation processes require a carbon source, for which plants and algal species are employed to reduce carbon dioxide via photosynthesis (using the energy of the sun) to the level of sugars and cell material. After harvesting, these end products are converted to ethanol by yeast fermentation (in the case of crops) or converted chemically to biofuels (in the case of algae). The overall energy conservation of these methods is highly inefficient and therefore demands large surface areas. In addition, the crop processes are rather labor-intensive, are demanding with respect to water consumption and affect food stock prices with adverse consequences for food supplies. A more remotely similar process is based on the conversion of solar energy into hydrogen. Also this process suffers from a severely decreased efficiency.
U.S. Pat. No. 6,699,696 describes a process of producing ethanol by feeding carbon dioxide to a cyanobacterial cell, especially a Synechococcus comprising a nucleic acid molecule encoding an enzyme enabling the cell to convert pyruvate into ethanol, subjecting said cyanobacterial cell to sun energy and collecting ethanol. This system has several drawbacks among others the expression system used is temperature sensitive which demands to adapt the production system for such regulation.
WO 2009/078712 describes a process of producing ethanol, propanol, butanol, acetone, 1,3-propanediol, ethylene or D-lactate and where appropriate intermediary compounds in the pathway leading to any of these organic compounds. The process is carried out by feeding carbon dioxide to a culture of cyanobacterial cells and subjecting the culture to light, wherein the cells are capable of expressing a nucleic acid molecule under the control of a regulatory system which responds to a change in the concentration of a nutrient in the culture which confers on the cell the ability to convert a glycolytic intermediate into the above-mentioned organic compounds and/or into intermediary compounds.
Erythritol is a four-carbon polyol (sugar alcohol) that is used as a sweetener in food and pharmaceutical industries. It is a naturally occurring substance, usually as a storage compound in seaweeds and fungi. Erythritol has roughly 65% of the sweetness of sucrose and is thus an attractive non-caloric substitute.
Erythritol is commercially produced via fermentation by various industries, such as Bolak Corporation (Whasung, Kyungki-do, Korea), Cargill Food & Pharm Specialties (Blair, Nebr., USA), and Mitsubishi Chemical Corporation (Tokyo, Japan). Glucose from chemically and enzymatically hydrolyzed wheat and corn starches is used as a major carbon source to produce erythritol by the fermentation of yeast-like fungi such as Torula sp. and Moniliella pollinis (Moon et al., 2010).
However, there is still a need for an improved production process of erythritol, preferably without the need of expensive or complicated starting materials, such as sugar, and which process does not have the drawbacks of existing processes such as those described here above.